DE102019219476A1 - Micromechanical device with cavern access through an ASIC substrate and manufacturing process - Google Patents

Abstract

The invention is based on a micromechanical device with an ASIC substrate (10, 11) and a MEMS substrate (20), which enclose a cavity (30), with a reclosed cavern access (60) with an integral closure (65) an outer surface of the device. The essence of the invention is that the cavern access runs from an outer surface of the ASIC substrate to the cavern through an access area (45) of the ASIC substrate which is cut out by ASIC structures (40). The invention also relates to a method for producing a micromechanical device.

Description

State of the art

The invention is based on a micromechanical device with an ASIC substrate and a MEMS substrate, which enclose a cavern, with a reclosed cavern access with an integral closure on an outer surface of the device.

In the case of combined MEMS components, ie an on-chip integration of several sensors, such as acceleration sensors and rotation rate sensors, different gas pressures are usually set in different caverns. According to the current state of the art, very low cavity pressures are used for rotation rate sensors, while higher pressures are regularly used for acceleration sensors. The implementation of the different pressures in different caverns can be done with the help of different techniques, for example the use of getter materials, as in the publication EP 2004 542 B1 is shown. It is also known to provide caverns with one access each and to close them again. For example, from the patents US 2016 0244 325 A1 and US 2016 0355 394 A1 the use of an oxide reseal process is known. From the German Offenlegungsschrift DE 10 2014 202 801 A1 the use of the laser reseal process is known.

In the laser reseal process, it is necessary to create an access opening to the cavern to be closed. So far, this has been done on the cap wafer and not on the sensor wafer. In micromechanical devices in which the ASIC wafer and sensor wafer are vertically integrated, that is to say an ASIC wafer is used as a cap for a MEMS wafer, it is desirable to find new concepts for opening the cavern.

The present invention disclosure shows a particularly efficient implementation option in which the reseal access takes place through the ASIC wafer. Alternative proposals, in which the reseal access for an ASICap component is created through the sensor wafer, are in the publications DE 201710207111 A1 and DE 102017215531 A1 shown.

task

It is the object of the present invention to create a micromechanical device with a cavity access through an ASIC substrate and a manufacturing method for this purpose.

Advantages of the invention

The invention is based on a micromechanical device with an ASIC substrate and a MEMS substrate, which enclose a cavern, with a reclosed cavern access with an integral closure on an outer surface of the device.

The essence of the invention is that the access to the cavern runs from an outer surface of the ASIC substrate to the cavern through an access area of the ASIC substrate that is cut out by ASIC structures.

An advantageous embodiment of the micromechanical device according to the invention provides that the closure consists of a solidified melt from the material on the outer surface of the ASIC substrate which surrounds the cavern access and is in particular a laser melt closure.

It is advantageous that the access to the cavern is designed in the form of a laser drilling. However, it is also advantageous that the access to the cavern is designed in the form of an anisotropic etching channel.

An advantageous embodiment of the micromechanical device according to the invention provides that the device has a recess with a base on the outer surface of the ASIC substrate and the cavern access with the closure is arranged on the base.

An advantageous embodiment of the micromechanical device according to the invention provides that the ASIC substrate is thinned back.

1. A: Bereitstellen eines ASIC-Substrats mit einem Zugangsbereich, der von ASIC Strukturen ausgespart ist;
2. B: Bonden des ASIC-Substrats mit einem MEMS Substrat, wobei die ASIC-Strukturen an die Kaverne angrenzen;
3. C: Herstellen eines Kavernenzugangs durch Herstellen einer durchgehenden Ausnehmung von einer äußeren Oberfläche des ASIC-Substrats bis zur Kaverne; D: Wiederverschließen des Kavernenzugangs mit einem stoffschlüssigen Verschluss an der äußeren Oberfläche des ASIC-Substrats.

The invention also relates to a method for producing a micromechanical device with an ASIC substrate and a MEMS substrate, which enclose a cavity, with the steps:

1. A: Providing an ASIC substrate with an access area that is cut out by ASIC structures;
2. B: bonding the ASIC substrate to a MEMS substrate, the ASIC structures adjoining the cavern;
3. C: producing a cavern access by producing a continuous recess from an outer surface of the ASIC substrate to the cavern; D: Reclosing the access to the cavern with an integral closure on the outer surface of the ASIC substrate.

An advantageous embodiment of the method according to the invention includes that after in step A and before step B a blind hole is made in the access area of the ASIC substrate, in step B the ASIC substrate is bonded to the MEMS substrate in such a way that the blind hole forms part of a cavern, and in step C for production A trench is introduced into the continuous recess from the outer surface of the ASIC substrate to the blind hole. It is advantageous that the blind hole is made by means of an etching process.

An advantageous embodiment of the method according to the invention provides that the trench is introduced by means of an etching process. It is particularly advantageous that at least one further trench for a through contact is also introduced by means of the etching process.

An advantageous embodiment of the method according to the invention provides that in step C the cavern access is established by laser drilling. It is advantageous that, in step D, the cohesive closure is produced by means of laser melting.

An advantageous embodiment of the method according to the invention provides that, before step D, a recess with a base is produced on the outer surface of the ASIC substrate by means of an etching process and the cavern access is arranged on the base.

It is advantageous that the ASIC substrate is thinned on the outer surface after step B, in particular by grinding and / or chemical-mechanical polishing.

It is also advantageous that after step D the ASIC substrate is planarized on the outer surface, in particular by grinding and / or chemical-mechanical polishing.

The invention allows the use of laser reseal technology for a combined MEMS component with an ASIC cap with several caverns with different pressures, but is not restricted to this.

The essence of the invention consists in a manufacturing method for a cavern access for realizing the laser reseal process in ASIC cap technology for setting a defined gas pressure in at least one cavern of a micromechanical device.

When using the ASIC cap technology, the MEMS wafer, for example a sensor wafer, is connected directly to the ASIC wafer. The previous approach in the prior art of creating the cavern access in the cap wafer cannot be implemented without further measures due to the layers and integrated circuits present in the ASIC. A production of the cavern access through the sensor wafer requires additional process steps or a very thin MEMS wafer maximum 150 µm. However, this would significantly limit the usability of the finished MEMS component, since important properties of the sensor, such as bending sensitivity, depend directly on the thickness of the sensor (including the cap). Therefore, such a heavily thinned-back sensor with cavern access through the sensor wafer could not be used for all applications, in particular highly accurate inertial sensors.

With the present invention, the limitation of the sensor thickness when using a laser reseal process in ASIC cap technology is overcome by allowing cavern access through the ASIC wafer by means of the method according to the invention.

The method according to the invention has a number of advantages. The ASIC wafer generally has a smaller layer thickness than the sensor wafer. This shortens the process time for creating the cavern access. If this is for example. created with a trench process, this will be more cost-effective. The procedure does not require any changes in the MEMS process. All process steps required for reclosing the cavern access take place in the ASIC wafer. This avoids complex additional process steps in the MEMS wafer. The subsequent processes after the actual reclosing are easy to carry out, as there is no large topography of the wafer surface, such as deep open trenches, on either the MEMS or ASIC side. According to the invention, the surface of the ASIC can be well planarized after reclosing.

The wafers are therefore very well prepared for further processes in terms of handling and further processing, such as the creation of through-silicon vias (TSV) in particular.

In an advantageous embodiment of the method, the trenching for creating the cavern access and for creating TSV trenches can be carried out in a common process step, which is particularly cost-efficient.

Figure list

• 1 shows an ASIC substrate with an access area that is cut out by ASIC structures.
• 2 shows schematically the ASIC substrate with the access area in which a blind hole is made.
• 3 shows schematically the ASIC substrate with a MEMS substrate bonded to it, which enclose a cavity, the blind hole forming part of the cavity.
• 4th schematically shows a micromechanical device according to the invention in a first exemplary embodiment with etched cavern access.
• 5 shows schematically the ASIC substrate with a MEMS substrate bonded to it, which enclose a cavity, the access area still being unprocessed.
• 6th schematically shows a micromechanical device according to the invention in a second exemplary embodiment with laser-drilled cavern access.
• 7th schematically shows a micromechanical device according to the invention in a third exemplary embodiment with cavern access in a recess.
• 8th schematically shows a micromechanical device according to the invention in a fourth exemplary embodiment with a planarized outer surface of the ASIC substrate.
• 9 shows schematically the ASIC substrate with the MEMS substrate bonded to it as well as etched trenches for the cavern access and for TSVs.
• 10 schematically shows a micromechanical device according to the invention in a fifth exemplary embodiment with a planarized outer surface of the ASIC substrate, TSVs and rear-side contacts.
• 11 shows schematically the method according to the invention for producing a micromechanical device with an ASIC substrate and a MEMS substrate, which enclose a cavern.

description

1 shows an ASIC substrate with an access area that is cut out by ASIC structures.

The necessary cavern access for the laser reseal is realized according to the invention by the ASIC wafer. As a prerequisite for this, the ASIC must have an area in which the creation of the cavern access does not damage the ASIC structures or the integrated circuit. There is an area for this 45 of a few µm ² , typically in size 30th × 30 µm to 50 × 50 µm ² (more generally: 10 × 10 µm ² to 100 × 100 µm ² ), left out of the active circuit. The associated loss of space is very low. With an ASIC size of e.g. B. 2 mm ² , the loss of area through the access to the cavern corresponds to only approx. 0.1%. 1 shows schematically an ASIC substrate 10 with ASIC structures 40 on one side, symbolized by a layer structure with metal conductor track levels and the passivation layers (oxides, nitrides). An access area 45 is excluded from the ASIC structures.

The creation of a cavern access through the ASIC wafer, prepared with the recessed access area, can be done in various ways, namely firstly by means of etching through the ASIC, preferably with a trench process (Deep Reactive Ion Etching) or secondly by means of laser drilling through the ASIC.

The creation of the cavern access through the ASIC by means of etching technology, for example by means of plasma etching, requires the etching process to be adapted to the materials to be etched. In the case of an ASIC, there are essentially two types of materials that have to be removed: silicon in the area of the substrate and dielectrics (silicon oxide, silicon nitride, doped silicon oxide) in the area of the layer structure of the ASIC.

The area already mentioned above which is left out of a circuit is designed in such a way that there are no metals in this area, only dielectrics. This has the great advantage that the etching process for removing these layers is not contaminated with metal and, in addition, the required etching properties can be restricted to the dielectric material group.

The cavern access will now be created in the ASIC in several steps. For this purpose, the area of the recess of ASIC structures is first removed using etching technology. This is done, for example, by structuring by means of photolithography and subsequent dry etching. 2 shows schematically the ASIC substrate 10 with the access area 45 in which a blind hole 62 is introduced.

The ASIC prepared in this way is now bonded to a MEMS wafer. For this purpose, z. B. a eutectic bonding process, a thermocompression bonding or a seal glass (glass frit) bonding process can be used.

3 shows schematically the ASIC substrate 10 with a MEMS substrate bonded to it 20th who have favourited a cavern 30th enclose, with the blind hole 62 forms part of the cavern. A micromechanical structure is located on the MEMS substrate in the cavity 50 arranged.

The ASIC substrate is then thinned to typically 100 µm and a trench is etched into the ASIC substrate for access to the cavern. The resulting cavern access is typically smaller in diameter than the area previously exposed by the active ASIC side, namely the blind hole 62 , in the oxide / nitride stack, as well as in the following 4th indicated. The cavern access is used to set a defined gas pressure in the MEMS cavern and is then particularly preferably sealed using the laser reseal technique. The result is in 4th shown. Other locking techniques, e.g. B. oxide reseal are also possible.

4th schematically shows a micromechanical device according to the invention in a first exemplary embodiment with etched cavern access. The device has a thinned ASIC substrate 11 and a MEMS substrate 20th on what a cavern 30th enclose. ASIC structures 40 point to the cavern. There is a micromechanical structure in the cavern 50 packed in an atmosphere with a certain pressure and composition. The device has a cavern access 60 in the form of an anisotropic etching channel with a trench 64 on that in a blind hole 62 opens, which is part of the cavern. The cavern access thus runs through an access area 45 in the ASIC, which is free of ASIC structures 40 is. The access to the cavern has a cohesive seal 65 on.

An alternative to the method described, in particular to the first etching of the dielectric layers from the active ASIC side and the subsequent etching of the substrate from the wafer rear side, is to etch the substrate including the dielectric layers from one side of the wafer. This can be done both before and after the bonding process.

In the process of completely etching the cavern access before bonding, it should be noted that processing of the wafers is only possible to a limited extent. In particular, the wafers are usually transferred by vacuum suction on the carrier, but this is no longer possible with a wafer with holes.

With the variant of etching the cavern opening through the ASIC substrate and the dielectric layers after bonding, the reduced selectivity and thus possible damage to the structures in the cavern must be taken into account. At the moment the cavern access penetrates the cavern, the etching gas, which in this case particularly etches dielectrics, can attack all of the surrounding dielectrics of the ASIC and also of the MEMS. Since overetching cannot be avoided due to process fluctuations (both from wafer to wafer and due to the inhomogeneity of the etching rate across the wafer diameter), damage to the dielectric layers on the ASIC wafer or the MEMS wafer is to be expected. Additional measures would have to be taken against this.

For the reasons mentioned, the manufacturing process described first, removing the dielectrics before bonding and etching the ASIC substrate after bonding, is preferred.

In order to simplify the manufacturing process of the cavern opening, a laser drilling process can be used instead of the etching process. In this context, laser drilling is understood to mean a method that enables material to be removed using a laser. Such procedures are also known as laser ablation. In this process, the ASIC wafer with the access area created in it 45 pointing to the MEMS wafer, bonded to the MEMS wafer. 5 shows schematically the ASIC substrate 10 with a MEMS substrate bonded to it 20th who have favourited a cavern 30th enclose, with the access area 45 is still unprocessed.

Then the cavern access is made by means of laser drilling 60 through the ASIC substrate 10 and the dielectric layers are made. The great advantage of laser drilling compared to etching is the non-selectivity of laser drilling. I. E. Irrespective of the materials used (metals, silicon, dielectrics, silicon oxide ...), material can be removed by means of laser drilling. It is therefore not necessary in this method that in the recessed access area 45 only dielectrics are present, metals can also be present. This facilitates the construction of the ASIC, since due to the design rules of the ASIC manufacturer, certain levels of metal filling must not be fallen below or exceeded in each metal level.

6th schematically shows a micromechanical device according to the invention in a second exemplary embodiment with laser-drilled cavern access.

The device is shown after laser drilling and subsequent closure of the cavern access using laser reseal or similar Procedure, e.g. B. Oxide Reseal. The device is similar to that in 4th shown variant. However, in 6th the cavern access 60 Due to the laser drilling process, the diameter in the ASIC substrate wafer is almost unchanged 10 and in the metal-oxide layer stack (in 6th are in the access area 45 only dielectrics shown). In the MEMS wafer 20th It may be necessary to take precautions so that the laser beam does not damage sensitive MEMS structures when it breaks through the metal-oxide stack of the ASIC. This is ensured by a suitable location of the cavern access, which is generally arranged laterally at a distance from sensitive MEMS structures. Such details are for the sake of simplicity in the 5 and 6th not taken into account.

Regardless of the manufacturing method by means of etching or laser drilling, an uneven surface is created at the closed cavern access when using the laser reseal, see 4th and 6th . This topography can be disadvantageous for further processing because the transfer of the wafers is made more difficult. This makes it difficult or impossible to suck in the wafer by means of a vacuum. In addition, the pressure points that arise at raised points on the uneven surface can damage the closure of the cavern access.

It is therefore advantageous to lower the closure. For this purpose, it is beneficial to create a recess on the outer surface, i.e. on the back of the ASIC, before introducing the cavern access. 7th schematically shows a micromechanical device according to the invention in a third exemplary embodiment with cavern access in a recess. A device similar to that in FIG 6th shown. Deviating from this, however, the ASIC 10 a recess on its back 70 on, which is so deep that the cohesive closure 65 of cavern access 60 does not protrude beyond the outer surface on the rear of the ASIC.

It is also advantageous to planarize the closure, for example using grinding processes or also CMP processes (Chemical Mechanical Polishing). 8th schematically shows a micromechanical device according to the invention in a fourth exemplary embodiment with a planarized outer surface of the ASIC substrate. The cohesive closure 65 is leveled thereby.

The combination of the two process steps from the 7th and 8th , i.e. first lowering the closure and subsequent planarization, is possible. This combination is particularly advantageous because the planarization process works much better (with fewer defects and more homogeneously with regard to the removal rate) if the grinding or the CMP process is carried out on a large-area stressed surface and not on individual bumps that are extremely small compared to the total area of the wafer like the ones in the 4th and 6th devices shown would be the case.

After surface grinding (state of 8th ) the wafers are in an optimal condition in terms of handling and further processing. In particular, advanced packaging processes can now be carried out particularly easily and reliably on the almost topography-free surface. This includes, for example, the creation of vias (TSVs) as well as passivation layers, metal rewiring (redistribution layer, RDL) and solder balls. With these processes, the electrical signals can be brought from the active ASIC side (facing the cavern) to the rear side of the ASIC (TSVs), rewired on the rear side (RDL) and finally connected to a circuit board via the solder balls.

Applying TSVs requires etching the ASIC substrate. Since the creation of the cavern access by etching ( 4th ) the ASIC substrate is also etched, this step can be carried out in an advantageous embodiment of the invention together with the etching of further trenches for TSVs. This is particularly economical since the etching of TSV trenches and cavern access can be carried out in one step.

9 shows schematically the ASIC substrate with the MEMS substrate bonded to it as well as etched trenches for the cavern access and for TSVs. The device is similar to that below 4th described before resealing. The device, however, has next to the trench 64 for access to the cavern 60 still more trenches 66 for vias (TSVs). The other trenches 66 end on TSV landing pads 42 .

1. i) Einstellen eines ersten Gasdrucks,
2. ii) Laser-Reseal des ersten Kavernenzugangs, anschließend
3. iii) Einstellen eines zweiten Gasdrucks und
4. iv) Laser-Reseal des zweiten Kavernenzugangs).

A further embodiment of the invention (not shown in the figure) includes that if there are several separate caverns on a chip, for example for a rotation rate sensor and an acceleration sensor, several cavern accesses are created simultaneously via the trench process for the cavern access (i.e. in the example one for each the rotation rate sensor and the acceleration sensor), but these are gradually closed with different gas pressures by means of two successive laser reseal processes. One possible process sequence would be

1. i) setting a first gas pressure,
2. ii) Laser reseal of the first cavern access, then
3. iii) setting a second gas pressure and
4. iv) Laser reseal of the second cavern access).

The planarization process that follows, optionally, levels the topography created during the laser reseal for both accesses at the same time. In an advantageous manner, with only very little additional effort (only process steps iii), iv) are additionally required), a very well-defined and, if necessary, particularly high or particularly low internal pressure can also be set for a second cavern.

10 schematically shows a micromechanical device according to the invention in a fifth exemplary embodiment with a planarized outer surface of the ASIC substrate, TSVs and rear-side contacts.

After cutting trenches together 64 for cavern access 60 and TSV trenches 66 The reseal process and the (optional) planarization process are carried out first, followed by the advanced packaging process. Etching is typically used in the TSV 66 A dielectric is applied to the side walls for insulation, the insulation is opened at the bottom of the TSV trench around a metal pad 42 in the ASIC, and in the next step the TSV trenches are completely or partially filled with metal. The metallization of the side walls can advantageously be carried out according to the prior art at the same time (i.e. without separate layer deposition) for the metallization of the metal rewiring (RDL) 80 on the back of the ASIC for contacting the solder balls 90 be used.

11 shows schematically the method according to the invention for producing a micromechanical device with an ASIC substrate and a MEMS substrate, which enclose a cavern.

1. A: Bereitstellen eines ASIC-Substrats mit einem Zugangsbereich, der von ASIC Strukturen ausgespart ist;
2. B: Bonden des ASIC-Substrats mit einem MEMS Substrat, wobei die ASIC-Strukturen an die Kaverne angrenzen;
3. C: Herstellen eines Kavernenzugangs durch Herstellen einer durchgehenden Ausnehmung von einer äußeren Oberfläche des ASIC-Substrats bis zur Kaverne;
4. D: Wiederverschließen des Kavernenzugangs mit einem stoffschlüssigen Verschluss an der äußeren Oberfläche des ASIC-Substrats.

The procedure includes the essential steps:

1. A: Providing an ASIC substrate with an access area that is cut out by ASIC structures;
2. B: bonding the ASIC substrate to a MEMS substrate, the ASIC structures adjoining the cavern;
3. C: producing a cavern access by producing a continuous recess from an outer surface of the ASIC substrate to the cavern;
4. D: Reclosing the access to the cavern with an integral closure on the outer surface of the ASIC substrate.

List of reference symbols

10

ASIC substrate

11

thinned ASIC substrate

12th

Part of the substrate removed from the back

20th

MEMS substrate

30th

cavern

40

ASIC structure

42

TSV pads

45

Access area

50

MEMS structure

60

Cavern access

62

Blind hole

64

dig

65

Clasp

66

further trench for via

70

Recess

80

Metal rewiring (RDL)

90

Solder ball

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 2004542 B1 [0002]
• US 20160244325 A1 [0002]
• US 20160355394 A1 [0002]
• DE 102014202801 A1 [0002]
• DE 201710207111 A1 [0004]
• DE 102017215531 A1 [0004]

Claims (16)

Micromechanical device with an ASIC substrate (10, 11) and a MEMS substrate (20), which enclose a cavity (30), with a reclosed cavern access (60) with an integral closure (65) on an outer surface of the device, characterized in that the access to the cavern runs from an outer surface of the ASIC substrate to the cavern through an access area (45) of the ASIC substrate which is cut out by ASIC structures (40). Micromechanical device according to Claim 1 , characterized in that the closure (65) consists of a solidified melt from the material on the outer surface of the ASIC substrate (10, 11) which surrounds the cavern access (60) and is in particular a laser fusible link. Micromechanical device according to Claim 1 or 2 , characterized in that the cavern access (60) is designed in the form of a laser drilling. Micromechanical device according to Claim 1 or 2 , characterized in that the cavern access (60) is designed in the form of an anisotropic etching channel. Micromechanical device according to one of the Claims 1 to 4th , characterized in that the device has a recess (70) with a floor on the outer surface of the ASIC substrate (10, 11) and the cavern access (60) with the closure (65) is arranged on the floor. Micromechanical device according to one of the Claims 1 to 5 , characterized in that the ASIC substrate (11) is thinned back. Method for producing a micromechanical device with an ASIC substrate and a MEMS substrate, which enclose a cavity, with the steps: A: Providing an ASIC substrate with an access area that is cut out by ASIC structures; B: bonding the ASIC substrate to a MEMS substrate, the ASIC structures adjoining the cavern; C: producing a cavern access by producing a continuous recess from an outer surface of the ASIC substrate to the cavern; D: Reclosing the access to the cavern with an integral closure on the outer surface of the ASIC substrate. Method for producing a micromechanical device according to Claim 7 , characterized in that - after step A and before step B, a blind hole is made in the access area of the ASIC substrate; - In step B, the ASIC substrate is bonded to the MEMS substrate in such a way that the blind hole forms part of a cavern; and in step C a trench is made from the outer surface of the ASIC substrate to the blind hole in order to produce the continuous recess. Method for producing a micromechanical device according to Claim 8 , characterized in that the blind hole is made by means of an etching process. Method for producing a micromechanical device according to one of the Claims 7 to 9 , characterized in that in step C the access to the cavern is established by laser drilling. Method for producing a micromechanical device according to one of the Claims 8 or 9 , characterized in that the trench is introduced by means of an etching process. Method for producing a micromechanical device according to Claim 11 , characterized in that at least one further trench for a via is also introduced by means of the etching process. Method for producing a micromechanical device according to one of the Claims 7 to 12th , characterized in that in step D the cohesive closure is produced by means of laser melting. Method for producing a micromechanical device according to one of the Claims 7 to 13th , characterized in that, before step D, a recess with a floor is produced on the outer surface of the ASIC substrate by means of an etching process and the cavern access is arranged on the floor. Method for producing a micromechanical device according to one of the Claims 7 to 14th , characterized in that the ASIC substrate after step B on the outer Surface is thinned, in particular by grinding and / or chemical-mechanical polishing. Method for producing a micromechanical device according to one of the Claims 7 to 15th , characterized in that the ASIC substrate is planarized after step D on the outer surface, in particular by grinding and / or chemical-mechanical polishing.

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